Conventionally, a pressure regulating circuit is known in which a workpiece attached to the tip of a piston rod can be elevated or lowered by a slight external force, just by adjusting the pressure inside an working chamber of a pneumatic cylinder to counteract the force exerted against the workpiece.
As shown in FIG. 9, in a conventional pressure regulating circuit, a pressure chamber 8 of a main valve 6 is connected to a working chamber 4 of a pneumatic cylinder 2. The pressure chamber 8 is connected to and disconnected from, via an air supply valve member 12, an air supply chamber 10 which is connected to a pressurized air supply R. An exhaust chamber 14, which is open to the outside air, is connected to and is disconnected from the pressure chamber 8 by means of an exhaust valve member 16.
A piston chamber 18 is provided above and independent of the exhaust chamber 14, and is divided into a control chamber 22 and a piston pressure chamber 24 by a pressure control piston 20. A piston rod 26 penetrating the pressure chamber 8 is connected to the pressure control piston 20. When the piston rod 26 lowers, the air supply valve member 12 is pressed down, thereby interconnecting the pressure chamber 8 and the air supply chamber 10. When the piston rod 26 is elevated, the exhaust valve member 16 is also elevated, thereby interconnecting the pressure chamber 8 and the exhaust chamber 14. The control chamber 22 is connected via an air pathway 28 to the pressure chamber 8. A port 30 of the piston pressure chamber 24 communicates with an auxiliary pressure chamber 402 of a control valve 400, and is opened via an orifice 404 to the outside air.
In the control valve 400 an auxiliary air supply chamber 406 is connected to the auxiliary pressure chamber 402 at one side and to the pressurized air supply R at the other side. The auxiliary pressure chamber 402 is connected to and disconnected from the auxiliary air supply chamber 406 by a valve member 408 having a shaft 408a penetrating through the auxiliary pressure chamber 402. A spring 410 is provided under the valve member 408 for urging the valve member 408 to close. An upper end 408b of the shaft 408a abuts the underside of a plate 418 mounted in the middle of a diaphragm 416, placed horizontally between an auxiliary control chamber 412 and a pressure spring chamber 414. The diaphragm 416 is urged downwardly by a pressure spring 420 provided in the pressure spring chamber 414, thereby lowering the valve member 408. The urging force of the pressure spring 420 can be adjusted with a handle 422. The auxiliary control chamber 412 is connected via the air pathway 28 to the pressure chamber 8 and then to the control chamber 22, such that the pressure from the pressure chamber 8 and the control chamber 22 is introduced to the auxiliary control chamber 412.
In the conventional pressure regulating circuit constructed as above, when the valve member 408 of the control valve 400 is pushed down by the pressure spring 420, the pressurized air flows from the supply R to the piston pressure chamber 24 of the main valve 6, and the pressure control piston 20 lowers, thereby pushing downward the air supply valve member 12. The pressurized air in turn flows from the supply R through the pressure chamber 8 to the working chamber 4, thereby allowing a piston P to rise together with a workpiece W. At this time the working chamber 4, the pressure chamber 8, the control chamber 22 and the auxiliary control chamber 412, which are interconnected to one another, have their pressure raised. When the pressure in the control chamber 22 surpasses that in the piston pressure chamber 24, the pressure control piston 20 is pushed upwards, thereby lifting up the piston rod 26. The air supply valve member 12 is in turn raised, disconnecting the air supply chamber 10 from the pressure chamber 8, while the exhaust valve member 16 is elevated, interconnecting the pressure chamber 8 and the exhaust chamber 14. The pressure in the working chamber 4 is reduced, and the piston P is lowered. When, by supplying the pressurized air to or discharging it from the pressure chamber 8, the pressure in the control chamber 22 and the pressure in piston pressure chamber 24 reach equilibrium, the piston rod 26 is brought into a neutral position. As shown in FIG. 8, the air supply valve member 12 and the exhaust valve member 16 are in a closed position. No air is supplied to or discharged from the pressure chamber 8 or the working chamber 4. Therefore, the piston P and the workpiece W are in a balanced condition without being raised or lowered. As aforementioned, when the pressure in the control chamber 22 and the pressure in the piston pressure chamber 24 reach equilibrium, the piston P attains a balanced condition.
The balanced condition of piston P is brought about by balancing the pressure in the control chamber 22 and the piston pressure chamber 24. The pressure in the piston pressure chamber 24 is regulated by the control valve 400. As shown in FIG. 8, when the urging force of the pressure spring 420 surpasses the pressure in the auxiliary control chamber 412 and the force of the spring 410, thereby pushing down the valve member 408, the auxiliary air supply chamber 406 is connected with the auxiliary pressure chamber 402 and the pressurized air flows toward the auxiliary pressure chamber 402. Since the pressurized air, having a larger airflow than the outflow amount from the orifice 404, flows toward the piston pressure chamber 24, the pressure in the piston pressure chamber 24 is increased.
Contrarily, when the pressure in the auxiliary control chamber 412 is increased to push the diaphragm 416 upwards, and the valve member 408 is elevated to disconnect the auxiliary air supply chamber 406 from the auxiliary pressure chamber 402, the pressurized air stops flowing into the piston pressure chamber 24. Air then flows out of the orifice 404, and the pressure in the piston pressure chamber 24 is reduced.
The pressure in the piston pressure chamber 24 is regulated by the urging force of the pressure spring 420 and by the pressure in the auxiliary control chamber 412. The pressure in the auxiliary control chamber 412 is equal to the pressure in the control chamber 22, the pressure chamber 8 and the working chamber 4. When the urging force of the pressure spring 420 is large, the pressure in the auxiliary control chamber 412 remains high, while the pressure in the piston pressure chamber 24 is in balance with that in the auxiliary control chamber 412. Contrarily, when the urging force of the pressure spring 420 is small, the pressure in the auxiliary control chamber 412 remains low, while the pressure in the piston pressure chamber 24 is in balance with that in the auxiliary control chamber 412.
Specifically, in order to place the piston P in a balanced condition, if the workpiece W provides a large load, by increasing the urging force of the pressure spring 420, the pressure in the working chamber 4 is increased. If the workpiece W provides a small load, by reducing the urging force of the pressure spring 420, the pressure in the working chamber 4 is decreased.
Under such a balanced condition, by exerting an upward external force to the workpiece W, the workpiece W is elevated, thereby reducing the pressure in the working chamber 4 and the control chamber 22. Accordingly, the pressure in auxiliary control chamber 412 is also reduced, thereby opening the control valve 400, and, as aforementioned, the pressurized air, having a larger airflow than the outflow amount from the orifice 404, flows toward the piston pressure chamber 24, thereby increasing the pressure in the piston pressure chamber 24. The pressure control piston 20 in turn lowers to push downwards the air supply valve member 12, and the pressurized air is supplied to the working chamber 4. Therefore, the workpiece W can be moved up with a slight external force.
Contrarily, under the aforementioned balanced condition, by exerting a downward external force on the workpiece W, the workpiece W is pushed downwards, thereby increasing the pressure in the working chamber 4, the control chamber 22 and the auxiliary control chamber 412. The control valve 400 is then closed, and the pressurized air stops flowing toward the piston pressure chamber 24. Since air flows out of the orifice 404, the pressure in the piston pressure chamber 24 is decreased. The pressure control piston 20 is in turn elevated to push the exhaust valve member 16 upwards, and the pressurized air is exhausted from the working chamber 4. The workpiece W can then be moved down with a slight external force.
When the workpiece W is raised or lowered with an external force and is stopped at a desired position, air is supplied to or exhausted from the pressure chamber 8. The pressure in the pressure control chamber 22 is then in balance with that in the piston pressure chamber 24. Thus, no air is supplied to or exhausted from the working chamber 4 and the workpiece W again attains a balanced condition.
As aforementioned, by adjusting the urging force of the pressure spring 420 according to the load of workpiece W, the piston P can be brought into a balanced condition. By exerting a slight external force on the workpiece W in the balanced condition, the workpiece W can be elevated or lowered.
In the conventional pressure regulating circuit, however, each time the workpiece W is replaced, the urging force of the pressure spring 420 should be adjusted again, which is troublesome.